Typical modulation/demodulation schemes start with foreknowledge of the intended use, the physical interconnect, and other system requirements. Because every manufacturer uses different approaches in their design, the market has multiple systems to communicate information from a device providing a useful function to its remote controller. Typical universal remote controllers simply record a visible spectra of information sent from a given controller then replay it. These are popular with optical systems such as infrared remote controls. With the advent of modern equipment, information is often exchanged prior to an operation between the device and the remote controller. Therefore, blindly recording the information is often not sufficient. In addition, because the information sent is parameterized (e.g. temperature settings), it is not feasible to emulate all variations of the parameters to arrive to all possible combinations.
In order to interface with such electrical systems, a true understanding of the underlying physical communication layer is necessary. In the past, most modulation/demodulation systems were focused on a given encoding scheme and multiple techniques for recovering the digital information were proposed. Most of these methods focused on Fourier transform analysis where the information was contained in the spectral analysis of the sinusoidal signal functions. These systems (mostly specialized ASICS) are pre-programmed for specific classes of signals to be modulated/demodulated following a specific standard. Because of their specificity, the encoding mechanisms are based on the Fast Fourier Transform (FFT) for demodulation and the Inverse Fast Fourier Transform (IFFT) for modulation, both discrete versions of the Fourier Transform (FT).
Using the Fourier Transform (FT), typical time-domain signals can be represented as a sum of sinusoidal functions in the spectral domain. However, the number of functions needed to represent any arbitrary signal including those with discontinuities is infinite (Gibbs phenomenon). Therefore, the Fourier coefficients are also infinite. In order for a decoding mechanism to apply to both continuous and non-continuous signals, it is necessary to preserve the frequency information as well as the temporal information of the signal. Due to the large constellation of points involved in decoding higher-order modulation schemes, more templates are required to properly detect the amplitude and phase changes. Thus, higher-order modulation schemes can require an enormous number of templates to be used when attempting to decode a signal. This is obviously very resource intensive and may be impractical for resource constrained applications.